We have made the serendipitous observation of primary Type IIb hyperlipoproteinemia in two male rhesus monkeys. In the experiments proposed in this application we seek to establish the heritability of this disorder, to further characterize the biochemical aberrations of this dyslipoproteinemia in rhesus monkeys, to obtain information on the means by which genetic modulation of plasma lipoprotein concentrations is expressed in both normal and hyperlipoproteinemic monkeys, to obtain information on the mechanism of inheritance of the disorder in rhesus monkeys if the defect can be shown to be heritable, and finally, to examine the feasibility of establishing a resource of these valuable primates for arteriosclerosis research.